1. Field of the Invention
This invention relates to a method for manufacturing a thin film magnetic head usable for a magnetic recording and reproducing drive device such as a magnetic disk drive device.
2. Related Art Statement
For realizing a high recording density in a magnetic disk using a thin film magnetic head, it is required that data amount (data density) to be restored in the unit area of the magnetic disk is enhanced. The surface recording density depends on performance of a recording element, and can be enhanced by shortening the gap length between the recording poles of the recording element.
The surface recording density can be also enhanced by increasing the track number to be recorded in the magnetic disk. The track number recordable in the magnetic disk is normally represented as “TPI (track per inch)”. The TPI performance of the recording element can be enhanced by downsizing the recording head to determine the width of the data track. The size of the recording head is normally known as a track width.
However, the shortening of the gap length between the recording poles and the narrowing of the track width decrease the magnetic flux in between the recording poles, resulting in the degradation of the overwrite performance. Therefore, in view of recording performance, the shortening of the gap length and the narrowing of the track width can not employed for a high density recording magnetic disk having a high coercivity Hc.
To solve this problem, the recording pole structure in which in a recording pole portion, a magnetic film having a high saturated magnetic flux density (a first magnetic film) is provided adjacent to a gap film and a second magnetic film having a smaller saturated magnetic flux density than the first magnetic film is provided on the first magnetic film is suggested and practically used. For example, the specification of U.S. Pat. No. 5,606,478 discloses that the part of the recording pole portion adjacent to the gap film is made of a magnetic material having a higher saturated magnetic flux, for example Ni55Fe45, than the magnetic material having a NiFe composition which is usually used for the pole portion of the above thin film magnetic head. However, the Ni55Fe45 material has only 1.4 T to 1.5 T, so that the recording performance is restricted.
In addition, the specification of Kokai Publication Kokai Hei 5-73839 (JP A 5-73839) discloses that an underfilm to plate a bottom magnetic core and a top magnetic core is made of a magnetic material having a higher saturated magnetic flux density than the magnetic materials constituting the bottom magnetic core and the top magnetic core.
In defining the track width of the recording pole portion using the above means in those related documents, the underfilm made of the magnetic film having the higher saturated magnetic flux density has to be etched by milling, etc. In the etching process, the part of the magnetic material constituting the underfilm is re-stuck on the side surfaces, etc. of the pole portion, resulting in the increase of the track width. This means the opposite result to the narrowing of the track width. Moreover, the re-stuck portion of the pole portion usually has inferior magnetic characteristics, so that the electromagnetic conversion characteristics of the pole portion is deteriorated.
If the underfilm is thinner, the re-sticking can be reduced. However, the thinner underfilm can not realize the essential object of enhancing the recording performance by making the underfilm of the magnetic material having a high saturated magnetic flux density. The above related documents do not disclose the means for solving the above problems due to the re-sticking.